Color display device and method

ABSTRACT

The color display according to the invention relates to a color display device and a color display method for color display by monochromatic display of data of respective colors in synchronism with sequential ON/OFF switching of three light sources for red, green and blue, respectively. In a preferred embodiment, the red, green and blue light sources are controlled to turn on and off in the order of red, green, blue and green in each unit period and to repeat the unit period.

TECHNICAL FIELD

[0001] This invention relates to a color display device and a color display method for representation of colors without using color filters, especially suitable for application to a field sequential system to represent colors by high-speed switching of three colored light sources of red, green and blue.

BACKGROUND ART

[0002] The field sequential color display method is a typical known method for displaying colors, i.e. representation of colors, without using color filters. The field sequential system uses three colored light sources of red, green and blue, and monochromatic display elements to represent colors by switching three colored light sources at a high speed and synchronously displaying data with monochromatic display elements. Monochromatic display elements may be either reflection-type elements or transmission-type elements.

[0003] Color display devices of the field sequential type not using color filters are applied to liquid crystal displays. Further, field sequential projectors have been realized as commercially available products because of some advantages, such as enabling a single-panel projector to attain a resolution equivalent to that of a three-panel projector not using the field sequential system, and simplifying the optical system. Furthermore, field sequential color display devices have been reported to be applied also to head mount displays that users can directly wear on eyes because compact and high-resolution color representation is possible.

[0004] In existing field sequential color display methods, red, green and blue light sources are sequentially turned ON and OFF in equally frequencies as shown in FIG. 2. For example, a round of lighting red→green→blue makes a unit period, and the unit period is repeated.

[0005] A color display method not using color filters, such as the field sequential system, needs display elements that can be switched very quickly. However, display elements tend to degrade in response when they are enhanced in resolution and enlarged in operative temperature range. Therefore, from the standpoint of the display elements, the switching cycle is preferably longer.

[0006] Regarding color display devices using the field sequential system, it is generally appreciated that users will sense flickers unless the ON/OFF frequency of each light source among red, green and blue light sources is shorter than {fraction (1/60)} second. This means that individual display elements must be switched at a frequency shorter than {fraction (1/180)} second, and this is against the requirement of a longer switching cycle as explained above.

[0007] It is therefore an object of the invention to provide a color display method and a color display device capable of preventing the problem of flickers even under a longer switching cycle of display elements.

[0008] A further object of the invention is to provide a color display method and a color display apparatus with which users are unlikely to sense flickers from color representation under the same switching cycle of display elements.

[0009] A still further object of the invention is to provide a color display method and a color display apparatus that can prevent users from that can remove user-conscious flickers from field sequential color representation even under a relatively long switching cycle of display elements.

DISCLOSURE OF INVENTION

[0010] Those objects can be accomplished by various aspects of the invention. According to the first aspect of the invention, there is provided a color display device for color display by using in combination ON/OFF switching of light sources for red, green and blue three colors with display elements for displaying data of respective colors in synchronism with the ON/OFF switching of said three color light sources, comprising: the green light source being turned on and off twice in a period after the red light source is turned on and before the light source is next turned on.

[0011] According to a further aspect of the invention, there is provided a color display device for color display by using in combination ON/OFF switching of light sources for red, green and blue three colors with display elements for displaying data of respective colors in synchronism with the ON/OFF switching of said three color light sources, comprising: the green light source being turned on and off twice in a period after the blue light source is turned on and before the blue source is next turned on.

[0012] According to a still further aspect of the invention, there is provided a color display device for color display by using in combination ON/OFF switching of light sources for red, green and blue three colors with display elements for displaying data of respective colors in synchronism with the ON/OFF switching of said three color light sources, comprising: the red, green and blue light sources being controlled to turn on and off in the order of red, green, blue and green in each unit period and to repeat the unit period.

[0013] In the unit period of the ON/OFF switching of the red, green and blue light sources, they may be turned on and off in the order of blue, green, red and green, or in the order of green, blue, green and red, or in the order of green, red, green and blue.

[0014] According to a yet further aspect of the invention, there is provided a color display method for color display by controlling display elements to display data of respective colors in synchronism with ON/OFF switching of light sources for red, green and blue three colors, comprising: turning the green light source twice in a period after the red light source is turned on and before the red light source is next turned on.

[0015] According to a yet further aspect of the invention, there is provided a color display method for color display by controlling display elements to display data of respective colors in synchronism with ON/OFF switching of light sources for red, green and blue three colors, comprising: turning the green light source twice in a period after the blue light source is turned on and before the blue light source is next turned on.

[0016] According to a yet further object of the invention, there is provided a color display method for color display by controlling display elements to display data of respective colors in synchronism with ON/OFF switching of light sources for red, green and blue three colors, comprising: turning the green light source twice in a period after the blue light source is turned on and before the blue light source is next turned on.

[0017] In any of the above-summarized methods, the unit period of turning the red, green and blue light sources on and off may be ON/OFF switching of blue, green, red and green, ON/OFF switching of green, blue, green and red, or ON/OFF switching of green, red, green and blue.

BRIEF DESCRIPTION OF DRAWINGS

[0018]FIG. 1 is a diagram that shows changes of optical transmittance of display elements and ON/OFF actions of red, green and blue light sources with time according to an embodiment of the invention.

[0019]FIG. 2 is a diagram that shows changes of optical transmittance of display elements and ON/OFF actions of red, green and blue light sources with time in an existing technique.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020]FIG. 1 is a diagram that shows changes of optical transmittance of display elements and ON/OFF actions of red, green and blue light sources with time in a preferred embodiment of the invention.

[0021] This embodiment is an application of the invention to field sequential color representation. Examples of products of this application include liquid crystal displays of projectors and head mount displays, among others.

[0022] As already known, the field sequential color display technique uses three colored light sources for red, blue and green, respectively, and monochromatic display elements capable of representing data while switching the data in synchronism with ON/OFF action of the respective light sources.

[0023] The existing techniques turn red, green and blue light sources ON and OFF respectively once in each unit period. However, the preferred embodiment shown here turns ON the green light source twice within the unit period such that lighting red→green→blue→green makes the unit period, and the unit period is repeated to turn ON and OFF the light sources in the order of, for example, red→green→blue→green→red→green→blue . . . as shown in FIG. 1. Therefore, in case of this embodiment, the green lighting cycle is one half that of the existing techniques.

[0024] The preferred embodiment shown here is based on the Inventor's knowledge that the critical frequency for users to sense flickers largely varies with color, namely, among red, green and blue. More specifically, with regard to red and blue, users will become insensitive to flickers when the ON/OFF frequency of their light sources reaches approximately 30 Hertz. In case of green, however, users will sense flickers up to the ON/OFF frequency of approximately 60 Hertz. That is, it is known that human eyes are more sensitive to flickers of green light more than red and blue light and therefore sense flickers of green light up to a frequency approximately twice that of red and blue light.

[0025] In the preferred embodiment shown here, lighting red→green→blue→green or lighting blue→green→red→green makes the unit period. If this period is {fraction (1/30)} second, for example, then the ON/OFF frequency of red and blue is 30 Hertz, and the ON/OFF frequency of green is 60 Hertz. As explained above, these values are effective ON/OFF frequencies for rendering users insensitive to flickers for respective colors. Thus the switching rate of the monochromatic display elements may be {fraction (1/20)} second.

[0026] That is, the preferred embodiment of the invention can slow down the display-switching rate of the monochromatic display elements than {fraction (1/180)} second that has been considered the limit for insensitivity to flickers with the existing techniques. Therefore, even when the display elements are enhanced in resolution and their operative temperature range is enlarged, flickers to human eyes can be prevented effectively. Additionally, since the switching frequency of the display elements may be lower, it contributes to saving the power consumption.

[0027] Even when the ON/OFF order of the light sources is red→green→green→blue→red→green→green→blue→red . . . or blue→green→green→red→blue→green→green→red→blue . . . , substantially the same effect as the above-explained lighting of red→green→blue→green as each unit period can be obtained. 

1. (Amended) a color display device for color display by using in combination on/off switching of light sources for red, green and blue three colors with display elements for displaying data of respective colors in synchronism with the on/off switching of said three color light sources, comprising: the green light source being turned on and off twice in a period after the red light source is turned on and before the light source is next turned on, thereby making it difficult for users to sense flickers.
 2. (Amended) A color display device for color display by using in combination ON/OFF switching of light sources for red, green and blue three colors with display elements for displaying data of respective colors in synchronism with the ON/OFF switching of said three color light sources, comprising: the green light source being turned on and off twice in a period after the blue light source is turned on and before the blue source is next turned on, thereby making it difficult for users to sense flickers.
 3. (Amended) A color display device for color display by using in combination ON/OFF switching of light sources for red, green and blue three colors with display elements for displaying data of respective colors in synchronism with the ON/OFF switching of said three color light sources, comprising: the red, green and blue light sources being controlled to turn on and off in the order of red, green, blue and green in each unit period and to repeat the unit period, thereby making it difficult for users to sense flickers.
 4. (Amended) A color display device for color display by using in combination ON/OFF switching of light sources for red, green and blue three colors with display elements for displaying data of respective colors in synchronism with the ON/OFF switching of said three color light sources, comprising: the red, green and blue light sources being controlled to turn on and off in the order of blue, green, red and green in each unit period and to repeat the unit period, thereby making it difficult for users to sense flickers.
 5. (Amended) A color display device for color display by using in combination ON/OFF switching of light sources for red, green and blue three colors with display elements for displaying data of respective colors in synchronism with the ON/OFF switching of said three color light sources, comprising: the red, green and blue light sources being controlled to turn on and off in the order of green, blue, green and red in each unit period and to repeat the unit period, thereby making it difficult for users to sense flickers.
 6. (Amended) A color display device for color display by using in combination ON/OFF switching of light sources for red, green and blue three colors with display elements for displaying data of respective colors in synchronism with the ON/OFF switching of said three color light sources, comprising: the red, green and blue light sources being controlled to turn on and off in the order of green, red, green and blue in each unit period and to repeat the unit period, thereby making it difficult for users to sense flickers.
 7. The color display device according to one of claims 1 through 7 wherein the display elements are monochromatic display elements of a reflection type or a transmission type.
 8. The color display device according to one of claim 1 through 6 which is display device of a field sequential color system.
 9. (Amended) A color display method for color display by controlling display elements to display data of respective colors in synchronism with ON/OFF switching of light sources for red, green and blue three colors, comprising: turning the green light source on twice in a period after the red light source is turned on and before the red light source is next turned on, thereby making it difficult for users to sense flickers.
 10. (Amended) A color display method for color display by controlling display elements to dispute data of respective colors in synchronism with ON/OFF switching of light sources for red, green and blue three colors, comprising: turning the green light source on twice in a period after the blue light source is turned on and before the blue light source is next turned on, thereby making it difficult for users to sense flickers.
 11. (Amended) A color display method for color display by controlling display elements to display data of respective colors in synchronism with ON/OFF switching of light sources for red, green and blue three colors, comprising: controlling the red, green and blue light sources controlled to turn on and off in the order of red, green, blue and green in each unit period and to repeat the unit period, thereby making it difficult for users to sense flickers.
 12. (Amended) A color display method for color display by controlling display elements to display data of respective colors in synchronism with ON/OFF switching of light sources for red, green and blue three colors, comprising: controlling the red, green and blue light sources controlled to turn on and off in the order of blue, green, red and green in each unit period and to repeat the unit period, thereby making it difficult for users to sense flickers.
 13. (Amended) A color display method for color display by controlling display elements to display data of respective colors in synchronism with ON/OFF switching of light sources for red, green and blue three colors, comprising: controlling the red, green and blue light sources controlled to turn on and off in the order of green, blue, green and red in each unit period and to repeat the unit period, thereby making it difficult for users to sense flickers.
 14. (Amended) A color display method for color display by controlling display elements to display data of respective colors in synchronism with ON/OFF switching of light sources for red, green and blue three colors, comprising: controlling the red, green and blue light sources controlled to turn on and off in the order of green, red, green and blue in each unit period and to repeat the unit period, thereby making it difficult for users to sense flickers.
 15. The color display method according to one of claims 9 through 14 which uses a field sequential system.
 16. (Amended) A color display method for color display by using in combination ON/OFF switching of light sources for red, green and blue three colors with display elements for displaying data of respective colors in synchronism with the ON/OFF switching of said three color light sources, comprising: the green light source being turned on plural times in each unit period of ON/OFF switching of light sources for red, green and blue three colors, thereby making it difficult for users to sense flickers.
 17. (Added) The color display device according to claim 8 wherein the display elements are liquid crystal display elements.
 18. (Added) The color display device according to claim 8 or 17 wherein the interval between OFF switching of any of the light sources and OFF switching of the light source of the next color is constant.
 19. (Added) The color display method according to claim 15 or 16 wherein the display elements are liquid crystal display elements.
 20. (Added) The color display device according to claim 15, 16 or 19 wherein the interval between OFF switching of any of the light sources and OFF switching of the light source of the next color is constant.
 21. (Added) The color display device according to claim 8 or 17 wherein all of said colors have an equal field span of time.
 22. (Added) The color display method according to claim 15 wherein all of said colors have an equal field span of time. 